1. Field of the Invention
The integrity of materials is well known to be affected by their environmental exposure. Testing apparatus has been designed to simulate environmental exposure. Numerous testers incorporate various light exposure devices to examine the degradation of materials by exposure to light, particularly ultraviolet light. Some of these testers also incorporate sprays or fogs, whereby the surfaces of the samples undergoing light exposure are wetted and allowed to dry as part of the cycle of testing along with light exposure. Most of such testers limit the extent of heating of the sample undergoing light exposure and moisture exposure, although limited sample heating is practiced in several testers. A few testers employ sample immersion as part of a test cycle with or without light exposures. Among immersion testers are several testing corrosion resistance of metals by immersion in a corrosive environment.
The light stability testers often are complex instruments designed to provide and/or monitor light of selected wavelengths for the testing.
Despite the number and variety of testers, there is no simple tester which subjects materials to the severe conditions which the environment sometimes imposes on materials.
These severe conditions are those encountered when the combination of conditions is such that the materials being tested are subjected to test influences which accentuate flaws in the performance of sample materials.
It has been found that these severe conditions are obtained when light exposure of the samples also includes alternate heat exposure and cooling while the sample also is undergoing intermittent prolonged water immersion followed by drying during heat and light exposure. The water immersion often includes immersion in water containing salts which accelerate metallic corrosion. In addition, the drying step in the gas phase often includes gaseous contaminates which accelerate metallic corrosion and/or which affect the strength of materials such as plastics.
This invention describes a simple tester which subjects samples to a combination of environmental exposures, including ultraviolet light, while a sample is being heated and cooled to cause material expansion and contraction while the sample also is undergoing prolonged water immersion followed by drying. The water frequently contains contaminants such as salts and hydrocarbon oils, and the gas phase also may contain contaminants such as gases present in polluted environments, including sulfur oxides, nitrogen oxides, oxides of carbon, ammonia, hydrogen sulfide, hydrocarbons and their oxidation products, halogens, halogenated hydrocarbons and their oxidation products. Where the material being tested is employed in a plant environment, the aqueous test liquid and the gas phase may contain other contaminants associated with a particular plant.
This invention is a device for measuring and testing the performance of a variety of coating materials including their ability to provide corrosion resistance while being subjected to environmental conditions including ultraviolet light, heating and cooling with associated expansion and contraction, immersion in water followed by drying, and exposure to chemicals in the water liquid phase as well as the gas phase including the effect of heat and water in the presence of these chemicals and in the presence of ultraviolet light.
While this invention is useful in testing all manner of coatings such as paints, lacquers, inks and primers on specified substrates, it also is useful in testing plastics, coated and uncoated textiles, rubbers and rubber coatings, packaging materials, as well as coated and uncoated metals, coated and uncoated woods, and adhesives for plastics, rubbers, metal, and wood products, and composite structures such as fiberglass reinforced plastics.
In the test apparatus of this invention, the combined effects of ultraviolet light, thermal expansion and contraction, water immersion, leaching and swelling are followed by heating to cause drying shrinkage in the presence of a corrosive vapor phase after immersion in a corrosive liquid phase. The light exposure is made so that it is accelerated by heat, and, with these effects acting in concert, failures are caused to appear in coatings, rubbers, plastics and adhesives. The results of these combined stringent conditions acting upon the samples establish performance ratings for the samples.
2. Description of the Related Art
The testing apparatus of the prior art for coatings and for corrosion resistance is listed in the following table:
______________________________________ U.S. Pat. No. Date Name ______________________________________ 1,458,941 6/23 Jameson 1,558,786 10/25 Buttolph 1,818,687 8/31 Buttolph 1,870,512 8/32 Jameson 1,969,606 8/34 Hall 2,195,726 4/40 Jameson 2,434,450 1/48 Williford 2,804,770 9/57 Gunther et al. 2,945,417 7/60 Caryl et al. 2,987,914 6/61 Gunther et al. 3,116,977 1/64 Grabowski et al. 3,224,266 12/65 Klippert 3,266,306 8/66 Arnold et al. 3,267,738 8/66 Korn, Jr. 3,327,536 6/67 Fitzgerald 3,353,025 11/67 Sturm 3,426,590 2/69 Suga 3,500,682 3/70 Newfield 3,501,942 3/70 Fitzgerald et al. 3,576,125 4/71 Kockott 3,582,282 6/71 Kampf et al. 3,664,188 5/72 Kockott 3,685,969 8/72 Young III 3,686,940 8/72 Kockott 3,886,791 6/75 Grossman 3,889,531 6/75 Suga 3,936,273 2/76 Powell 4,012,954 3/77 Klippert 4,069,019 1/78 Suga 4,092,122 5/78 Suga 4,282,181 8/81 Pierce 4,391,522 7/83 Schmid et al. ______________________________________
Brief comments about the exposure conditions of each prior art apparatus are included below, along with information on how the conditions employed differ from the teachings of the present invention:
U.S. Pat. No. 1,458,941 exposes samples to ultraviolet light from an electric lamp while cooling the samples with air flow and evaporative cooling. Heating of samples during light exposure is avoided, and there is no water immersion of samples.
U.S. Pat. No. 1,558,786 exposes samples to ultraviolet light with air flow and humidity controlled by baffles, samples are not exposed to heat, nor are they immersed in water.
U.S. Pat. No. 1,818,687 exposes samples to ultraviolet light but filters out heat producing rays. Samples can be exposed to different humidity and temperatures, but they are not exposed to intermittent heating and cooling nor to elevated temperatures or immersion in water.
U.S. Pat. No. 1,870,512 describes apparatus for directing light and heat onto samples which are subject to a water spray between intervals of light exposure and which are also subject to controlled atmospheric humidity. This prior art apparatus directs spray on one surface of a sample and does not provide for sample immersion, and its light and heat rays arise from the same source and air flow is employed to cool the chamber below its set point temperature.
U.S. Pat. No. 1,969,606 discloses an apparatus which tests color materials by exposure to light under controlled humidity and temperature. The sample is not immersed, and the temperature of the sample does not cycle.
U.S. Pat. No. 2,195,726 discloses a masking device for use in connection with the testing of samples of color for fastness to light. The exposure conditions mentioned are light rays only.
U.S. Pat. No. 2,434,450 describes a sample holder for use in accelerated light testing, which holder is curved to receive equal intensity of light from a substantially point source of light. The exposure conditions described employ light rays only.
U.S. Pat. No. 2,804,770 describes apparatus for exposing samples to intermittent light exposure. The samples are not immersed, nor are they heated.
U.S. Pat. No. 2,945,417 claims an apparatus for concentrating solar rays on materials using a mirror holding frame while blowing air over the sample surfaces to remove excess heat. A sample spray system and an air humidifier are mentioned, but no sample immersion is practiced, nor is there a controllable heat source employed.
U.S. Pat. No. 2,987,914 claims an apparatus for light exposure with two zones for fluid flow to cool or heat in a preselected manner. The apparatus does not provide for sample immersion, and intermittent heating and cooling are not effected.
U.S. Pat. No. 3,116,977 discloses an apparatus to screen corrosion inhibitors by immersing metallic test specimens into a heated bath of water having the inhibitor dissolved therein, withdrawing the metallic specimens and heating them, and continuing the periodic immersion and withdrawal for a substantial period. No light exposure is provided, however, and the specimens are heated by current through the specimen plates.
U.S. Pat. No. 3,224,266 claims an apparatus for testing samples under conditions such as humidity, rain, or complete immersion in liquid, heat and air circulation, as well as light and dark periods with controlled changeover between light and dark. It provides for heating with a heater source of warm air in addition to heat from the illumination source. This prior art apparatus does not provide a separate radiant heater, and the rapid sequencing of immersion (with cooling) followed by radiant heating cannot be achieved.
U.S. Pat. No. 3,266,306 describes an apparatus to test resistance of materials to humidity by exposing them to steam pressure in a chamber. No light exposure is practiced in this prior art patent.
U.S. Pat. No. 3,267,738 discloses a test unit to expose test specimens at high altitude conditions for known periods of time and to return them to a package for ground return. No radiant heating or sample immersion is disclosed.
U.S. Pat. No. 3,327,536 describes a testing unit for large structures with ultraviolet light and infrared ray sources. While rain simulation is included, there is no immersion in water, nor are rapid intermittent heating and cooling by immersion described.
U.S. Pat. No. 3,335,025 describes an apparatus for testing samples exposed to humidity and irradiation. Capacitance is employed to measure humidity at the sample. Sample immersion and radiant heating are not described.
U.S. Pat. No. 3,426,590 discloses an apparatus for exposing samples to light wavelengths, with different proportions of light of the various wavelengths. No immersion of samples or radiant heating are described.
U.S. Pat. No. 3,500,682 describes a weathering apparatus where the samples are exposed to light and to water vapor. The samples are not immersed, nor are they heated by an infrared heater in the vapor space. Samples are placed on a stationary mount.
U.S. Pat. No. 3,501,942 claims a process for accelerating paint weathering by spray wetting with deionized water, drying with an infrared source, and exposure to ultraviolet light. The composition of the energy in ultraviolet, visible light, and infrared is defined. The process does not mention sample immersion. The copending apparatus patent has not been issued.
U.S. Pat. No. 3,576,125 claims an apparatus for uniform heat or light irradiation using end loss radiation compensators. Immersion of samples in water is not mentioned.
U.S. Pat. No. 3,582,282 describes a process for accelerating the testing of pigmented paint films by radicals produced in a gas to which the films are exposed. The radicals are formed from water vapor by a high frequency source which is not used in the present application. Radiant heating and immersion with light irradiation are not employed in this prior art patent.
U.S. Pat. No. 3,664,188 claims an apparatus to accelerate testing by exposing samples to irradiation at super ambient pressures. The present application employs a gas phase at atmospheric pressure. This prior art patent does not provide for sample immersion and heating with light exposure.
U.S. Pat. No. 3,685,969 discloses an apparatus for testing the strength of specimens under corrosive conditions. Specimens under stress are subjected to intermittent immersion using gravity flow of corrosive fluid to and from a fixed tank with the specimens. Light irradiation is not mentioned, nor is radiant heating before immersion.
U.S. Pat. No. 3,686,940 claims an apparatus for exposing test samples to ultraviolet and visible light radiation by filtering the radiations to provide for removal of infrared radiation and conducting the heat away by cooling tubes with fins. Thus, heating of samples is avoided in this prior art patent.
U.S. Pat. No. 3,886,791 describes an apparatus for providing sample exposure to light, humidity, condensation, heat and/or atmospheric pollutants. Sample immersion and the heating by infrared radiation followed by immersion cooling are not described in this prior art patent.
U.S. Pat. No. 3,889,531 discloses a weather test apparatus where samples on a transverse rotary test support receive sunlight from focused mirrors, while being cooled by air flow through the center of the transverse support. Motors with cam switches rotate the sample support 90.degree. to provide exposure to rain as well as averaged light exposure on the four faces of the transverse support. Radiant heating of the samples followed by cooling by water immersion is not employed in this prior art patent.
U.S. Pat. No. 3,936,273 discloses an apparatus for determining the corrosion protection performance of a fluid. This apparatus rotates test specimens mounted on a shaft through the liquid and thereafter may maintain the test specimens for extended periods in the fluid prior to examination for the degree of corrosion. This prior art patent does not provide for irradiation by light or the radiant heating in the vapor space although the testing fluid bath may be cooled.
U.S. Pat. No. 4,012,954 claims an apparatus for testing light and weather-resisting properties of materials by employing a mirror reflecting infrared and passing ultraviolet and visible light from an illumination source together with a second mirror reflecting visible and ultraviolet light while transmitting the infrared portion. Samples on a horizontal support can be flooded with water, drained or water cooled, and may also be air cooled. In this prior art patent there is no infrared heater in the vapor space. Infrared heating is avoided.
U.S. Pat. No. 4,069,019 discloses an apparatus for spray corrosion testing in which the water seal groove on an open topped test tank having a lid to cover the test tank is provided with a flexible porous insert of a water absorbing material. The water seal groove of this application does not contain a flexible porous insert of a water absorbing material.
U.S. Pat. No. 4,092,122 discloses a corrosion testing machine in which specimens on a rotating annular frame receive spray from a tower at the center of a rotating column supporting the annular frame. No light expsure is provided, nor is sample immersion, nor is radiant heating in the vapor space.
U.S. Pat. No. 4,282,181 describes an apparatus for accelerated corrosion testing of parts in which the parts are lowered into a corrosive medium and then raised into a drying zone for predetermined, repetitive periods. Although infrared heating is employed, and although the test can be applied to paints, no mention of ultraviolet light exposure is made.
U.S. Pat. No. 4,391,522 claims an apparatus for determining light and weather resistance of samples, which apparatus is equipped with a radiation measuring probe to measure intensity and/or dosage in one of several pre-selected spectral regions. Radiant heating and cooling by sample immersion are not mentioned.